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The core element of the M112 is an 11.3kg carbon fiber composite tube, a single-round self-contained disposable launcher supported by a bipod stand and baseplate.[1] The tube incorporates RTM ports to connect it to the fire control system. The bipod can be set to launch the warhead horizontally or at increasing angles up until the vertical, depending on deployment.[1]

Fire control for the M112 varies according to mission. For defensive deployment, the weapon is attached to an APS-100 Fire Controller, an 800 Gb intelligent system capable of importing data from the local USCM sensor matrix, including any motion trackers, infrared scanners, lidar, radar and robot sentries in operation. The APS-100 can be set to either Autonomous or Command configurations.[2] When active, the unit analyses incoming sensor data, and if it positively identifies a target it will lock on with one or more missiles under its command.

If set to Command mode, upon identifying a target the APS-100 will pass a target lock indication to the connected operator's terminal, allowing the oeprator to either authorize launch or, if the target's identity is unclear, request a further Identification Friend Foe (IFF) interrogation.[2] If enabled for autonomous mode, the APS-100 will work through its target identification protocols to ensure that the locked-on target is an enemy before automatically launching an appropriate strike.[2] It is also possible to datalink the APS-100 into higher level assets, such as surveillance drones or artillery forward observers.

Offensively, the M112 HIMAT can be deployed in a direct fire mode by plugging an SR-90 infantry-operated target acquisition sight directly into the launcher.[2] The SR-90 is designed specifically for use with the M112, combining a passive thermal imaging sight with an active ultrasonic motion tracker. The sight plugs directly into the launch tube's RTM port, and has sufficient optic cable to allow the operator to safely fire the M112 from up to 150m away.[2] Once the operator has identified and locked onto the target with the sight, the information is passed to the missile and the weapon can be fired by depressing both the Safety and the Fire triggers on the sight simultaneously.[2] A new infantry sight, the SR-105, replaces the motion tracker with a millimeter-wave radar, allowing the missile to be targeted at soft targets such as bunkers.[3]

The HIMAT missile itself is a small, two-stage round with a range of 5,000m. The first stage launches the missile vertically into the air, while the second activates 1.5 seconds after launch to accelerate the missile almost instantly to speeds of Mach 4.5.[3] Within the nose of the missile is a multi-sensor seeker: a Boekhoven-Bonn infrared imager in the 8-12 µm range, a Thoreson millimeter-wave radar and superheterodyne receiver aerial for homing in on active radar jamming. The seeker scans the target vehicle upon approach and identifies the target's type and configuration from its onboard memory, either to assess the optimum point of attack or veer away if its has been accidentally launched at a friendly target.[3] The warhead itself, located behind the seeker assembly, is a 15cm tungsten kinetic penetrating rod surrounded by LX-28 explosive filling, which is detonated just before impact. The force of the explosion, combined with the hypervelocity of the missile, ensures penetration against all but the strongest tank armor.[3]

Despite it's intended purpose as an anti-armor weapon, the HIMAT is also somewhat successful at targeting low-flying aircraft such as dropships and helicopters. As a result, the USMC has begun allocating funds to develop a multi-purpose warhead for both the ground and air-defense role.[3]

Although a devastating weapon, the HIMAT's intelligence systems have been known to be "fooled" when facing previously-unknown vehicles. If a warhead misidentifies the weak point on enemy armor it may fail to score a kill; worse still, due to the limitations of the weapon's guidance system, subsequent missiles will repeatedly target for the same location on the vehicle, meaning they too will fail to cause significant damage.[3] Only reprogramming of the weapon's software with updated information will solve the problem.

When operating as part of a Marine Assault Unit, each line company includes a number of M112 HIMAT systems as part of their support weapons, which may be attached to its component rifle platoons.[4]